The present invention relates to systems and methods for controlling the flow of a conductive fluid over a surface, and more particularly to a system and method that uses magnetic and electric fields to create Lorentz forces that affect the flow of a conductive fluid in a controlled manner near the boundary layer of a control tile, or a matrix of control tiles, immersed in the conductive fluid. Even more particularly, the invention relates to the methods and apparatus used to fabricate control tiles that permit the active control of surface drag of a conductive fluid.
Conductive fluids naturally occur in many different settings. It is noted that, for purposes of this application, the term "fluid" is used in its broad scientific sense to connote a liquid or a gas. Wherever such a conductive fluid is encountered, there is typically a need or desire to move a vessel or other object through the conductive fluid using a minimal amount of energy. One way to meet this need is to design such vessel or object so that the conductive fluid flows over the surface thereof with a minimal amount of drag.
Perhaps the most common example of a conductive fluid is sea water, which covers a significant percentage of the earth's surface. Ocean-going vessels traveling through sea water, e.g., ships or submarines, must exert significant amounts of energy in order to successfully navigate through the sea water at a suitable speed. Hence, much attention has been directed over the years to optimally designing the hull or shape of an ocean-going vessel in order reduce the drag (friction) the fluid encounters as it passes over the surface of the vessel. Despite such efforts, however, there remains a continual need to further reduce the drag encountered by conductive fluids passing over the surface of such vessels to thereby make the movement of such vessels through the fluid more efficient.
As is known in the art, a viscous fluid, and a body completely immersed in the fluid, form a boundary layer at the body's surface when the fluid and the body move relative to each other. That is, the layer of fluid in contact with the body is essentially at rest, while in an area removed from the body, the fluid is moving at its free-stream velocity. The region between the body and that area is known as a boundary layer. Where the fluid is a conductive fluid, electromagnetic forces may be introduced into the boundary layer in an attempt to alter the boundary layer characteristics. See, e.g., U.S. Pat. No. 5,437,421.
In copending U.S. patent application Ser. No. 09/099,811, filed concurrently herewith, now U.S. Pat. No. 6,079,345; and in copending U.S. Pat. application Ser. No. 09/099,852, also filed concurrently herewith, now U.S. Pat. No. 6,059,236; there is disclosed a system, a preferred embodiment of which uses a tangential force panel, for actively controlling a conductive fluid flowing over a control tile, or an array of control tiles forming a control panel, using multiplexed current driving. As disclosed in the referenced patent applications, both of which are assigned to the same assignee as is the present application, and both of which are incorporated herein by reference, magnetic and electric fields are used in a controlled manner in order to create Lorentz forces that affect the flow of a conductive fluid near the boundary layer of a control tile, or a matrix of control tiles, immersed in a conductive fluid.
More specifically, the Lorentz forces created by the systems disclosed in the referenced applications combine to form a vortex wavefront, referred to as a "roller", that is transverse to the fluid flow direction. Such roller wavefront advantageously allows the drag of the conductive fluid over the matrix of control tiles to be controlled in a beneficial manner. The use of such vortex wavefronts, or rollers, in a beneficial way is referred to generally as ElectroMagnetic Turbulence Control (EMTC).
When a panel comprising a matrix of control tiles is immersed within a conductive fluid, the EMTC invention disclosed in the referenced patent applications may be used to render movement of the panel through the conductive fluid more efficient, i.e., with less drag. For example, when such an EMTC panel, or a pair of such panels, is attached to the hull of an ocean-going vessel moving through sea water, or to the shell of an airborne vessel moving through an ionized atmosphere, the forces created at the surface of such panels may be used to help make propulsion of the vessel more efficient (with less drag) and quieter (with less detectable sound), to help steer the vessel (by creating increased drag forces on one side of the vessel and reduced drag forces on the other side), or to help stop or slow down the vessel (by creating increased drag).
As taught in the referenced patent applications, the control tiles form control cells, with each control cell including a pair of electrodes and at least one permanent magnet. The pair of electrodes are coupled to a current source which biases the electrodes to cause an electrical current to flow from a positive electrode (anode), through the conductive fluid in which the cell electrodes are immersed, to a negative electrode (cathode). The current source may be time multiplexed to better control the direction of the current flow between adjacent electrodes. A plurality of n current sources, which n is an integer of at least two, may be employed to create n phases of current that allow optimum creation of the "rollers". The permanent magnet(s) generates a magnetic field which interacts with the electrical current to create a Lorentz force that creates the vortex wavefronts, or "rollers", which influence the flow of the conductive fluid, near the boundary of the control tile, e.g., reduces drag of the fluid as it flows over the tile surface.
In order to obtain beneficial use of the EMTC invention(s) described in the referenced patent applications, it is necessary to manufacture the EMTC control panels used with the invention. Such EMTC control panels contain the control tiles or control cells which allow the electrical currents and magnetic fields to be created and beneficially interact with each other in a way that creates the Lorentz forces needed to control the drag of a control surface through the conductive fluid. To this end, there is a continuing need for better and more optimum EMTC control panel designs, as well as improved control panel manufacturing techniques and procedures.